1. Field of the Inventive Concepts
The presently claimed and disclosed inventive concept(s) relates generally to heart monitoring devices and methods and, more particularly, but not by way of limitation, to devices, systems and software for generating and providing one or more 12-lead electrocardiograms utilizing only two electrodes.
2. Brief Description of Related Art
Electrocardiography has been used to study the electrical activity of the heart. Electrocardiograms (ECG) can be recorded or taken using electrodes placed on the skin of a patient. The electrical signals recorded between any two electrodes placed on the skin of the patient are referred to as “leads.” Varying numbers of electrodes and leads can be used to take the ECG. Exemplary numbers of leads used conventionally for taking ECGs are 3, 5, and 12 leads. For a standard 12-lead ECG, ten electrodes are used with six electrodes positioned on the chest and one electrode on each of the patient's arms and legs.
FIG. 1 is a pictorial representation of the 10 electrodes of a conventional electrocardiograph being placed on the patient for obtaining a standard 12-lead ECG. The electrode placed on the right arm is commonly referred to as RA. The electrode placed on the left arm is referred to as LA. The RA and LA electrodes are placed at the same location on the left and right arms, preferably but not necessarily near the wrist. The leg electrodes can be referred to as RL for the right leg and LL for the left leg. The RL and LL electrodes are placed on the same location for the left and right legs, preferably but not necessarily near the ankle.
FIG. 2 illustrates the placement of the six electrodes on the chest in the prior art arrangement with such electrodes being labeled V1, V2, V3, V4, V5, and V6. V1 is placed in the fourth intercostal space, for example between ribs 4 and 5, just to the right of the sternum. V2 is placed in the fourth intercostal space, for example between ribs 4 and 5, just to the left of the sternum. V3 is placed in the fifth intercostal space midway between electrodes V2 and V4. V4 is placed in the fifth intercostal space between ribs 5 and 6 on the left mid-clavicular line. V5 is placed horizontally even with V4 on the left anterior axillary line. V6 is placed horizontally even with V4 and V5 on the left mid-axillary line.
The electrocardiograph then calculates and outputs three limb lead waveforms. Limb leads I, II, and III are bipolar leads having one positive and one negative pole. Lead I is the voltage between the left arm (LA) and right arm (RA), e.g. I=LA−RA. Lead II is the voltage between the left leg (LL) and right arm (RA), e.g. II=LL−RA. Lead III is the voltage between the left leg (LL) and left arm (LA), e.g. III=LL−LA. Leads I, II and III are commonly referred to as “limb leads.”
Unipolar leads also have two poles; however, the negative pole is a composite pole made up of signals from multiple other electrodes. In a conventional cardiograph for obtaining a 12-lead ECG, all leads except the limb leads are unipolar (aVR, aVL, aVF, V1, V2, V3, V4, V5, and V6). Augmented limb leads (aVR, aVL, and aVF) view the heart from different angles (or vectors) and are determined from RA, RL, LL, and LA. For example, the augmented vector right (aVR) positions the positive electrode on the right arm, while the negative electrode is a combination of the left arm electrode and the left leg electrode, which “augments” the signal strength of the positive electrode on the right arm. Thus the augmented vector right (aVR) is equal to RA−(LA+LL)/2 or −(I+II)/2. The augmented vector left (aVL) is equal to LA−(RA+LL)/2 or (I−II)/2. The augmented vector foot (aVF) is equal to LL−(RA+LA)/2 or (II−I)/2.
The six electrodes on the chest of the patient are close enough to the heart that they do not require augmentation. A composite pole called Wilson's central terminal (often symbolized as CTW, VW, or WCT) is used as the negative terminal. Wilson's central terminal is produced by connecting the electrodes RA, LA, and LL together, via a simple resistive network, to give an average potential across the body, which approximates the potential at an infinite distance (i.e. zero). Wilson's central terminal, WCT, is calculated as (RA+LA+LL)/3.
FIG. 3 illustrates an example Lead I annotated to show PQRST waves generated by a 12-lead electrocardiograph. The identification and measurement of the PQRST waves based on the electrocardiogram is known in the art. FIG. 4 illustrates an example of a 12-lead electrocardiogram in a conventional format.
While a conventional 12-lead electrocardiogram gives very useful information concerning the health and condition of an individual's heart, the conventional electrocardiograph equipment is expensive and the procedure is not normally available in areas other than hospitals and medical doctors' offices. Therefore monitoring is not done frequently even in wealthy countries, and in poorer areas of the world an electrocardiograph may not even be available. To significantly reduce costs of obtaining an electrocardiogram, a 2-electrode electrocardiograph device as described in U.S. Pat. No. 8,301,232 was marketed. The 2-electrode electrocardiograph device utilizes a smart phone connected to and at least partially surrounded by a phone protective case incorporating and supporting the two electrodes. Such devices significantly simplify and reduce the cost of obtaining an electrocardiogram, although such an electrocardiogram does not include as much information as a 12-lead electrocardiogram produced by an electrocardiograph having 10 electrodes. The 12-lead electrocardiogram produced by the 10-electrode electrocardiograph offers additional and important heart-related information to the cardiologist, allowing the diagnosis of conditions like heart attacks (myocardial infarctions) that a single-lead ECG cannot do. It would be advantageous if a readily available and inexpensive device could generate and produce an electrocardiogram that substantially replicates the 12-lead electrocardiogram produced by a 10-electrode electrocardiograph.